Long waiting lists for entry into opioid maintenance treatment (OMT) exact a tremendous cost on both heroin-dependent people and society. This three-year health services research study, conducted within the context of a mobile opioid maintenance treatment program, seeks to examine the ability of interim maintenance treatment to facilitate entry into full service OMT programs, and to reduce heroin and cocaine use, HIV risk, and criminal behavior of heroin-dependent people on waiting lists in Baltimore City. Adult heroin-dependent subjects (N = 360) who meet FDA criteria for OMT and for whom no treatment slot is available, will be randomly assigned to either: a) interim treatment with LAAM, an opioid agonist that can be administered thrice weekly; b) interim treatment with methadone; or c) standard waiting list condition (no treatment control group). Interim treatment will consist of LAAM or methadone therapy, with counseling on an emergency-only basis. All participants will be registered on the mobile program's waiting list for full service OMT and will be encouraged to call the 11 existing full service OMT programs in Baltimore City for waiting list placement and treatment entry. Following FDA guidelines, all interim treatment subjects who have not gained entry into full service OMT programs by 120 days from study entry will be admitted to one of Baltimore City's OMT programs, by explicit agreement with the Baltimore City's substance abuse authority. Control subjects will gain entry through the usual waiting list procedures in Baltimore City. Outcome will be assessed by measuring the percentage of subjects who enter full service OMT programs, as well as changed in participants' drug use, HIV-risk behavior, and criminal activity, with assessments obtained at baseline, at the time of full service treatment entry or 120 days from baseline for those subjects who do not enter full service treatment, and six months thereafter. We hypothesize that subjects receiving interim opioid maintenance treatment will have superior outcomes to waiting list controls. Furthermore, we hypothesize that LAAM interim subjects will have superior outcomes to methadone interim subjects, because LAAM's reduced clinic reporting schedule will facilitate interim program adherence and retention. The results of this study will provide a definitive determination of the effectiveness of a strategy to improve the OMT service delivery system by reducing barriers to treatment entry.